Empty, isset and is of PHP_ Null difference

PHP Three functions are provided for testing variable values , Namely isset(),empty(),is_null(), They all return Boolean values , But there are differences .

View through the following table ：

 

Contrast item	isset() Method	empty() Method	is_null Method
""（ An empty string ）	true	ture	false
" "( A space )	true	false	false
FALSE	true	true	false
TRUE	true	false	false
array()( An empty array )	true	true	false
NULL	false	true	true
"0"( character string 0)	true	true	false
0( integer 0)	true	true	false
0.0( floating-point )	true	true	false
$a( Unassigned variables )	false	true	false

1、isset() Function is used to detect whether a variable has been declared and the value is not NULL, That is, only when the value is not NULL Returns true when

2、empty() It is used to check whether a variable is empty. If there are the following conditions, it returns the true value ：

    1） An empty string

    2）false

    3） An empty array

    4）NULL

    5）0

    6）0.0

    7)unset The next variable

    8） character string 0

3、is_null() Used to determine whether the variable content is null value , The only condition for returning a true value is that the variable is null when , So he is. isset() The inverse function of , It can also be seen from the above table